1

Options

for the

storage of

renewable

energy

Prof Daniel Favrat

Energy Center

Ecole Polytechnique

Fédérale de Lausanne

RENEWABLE ENERGIES Allows seasonal cold storage

Allows seasonal

fuel storage

MONTHLY FINAL ENERGY DEMAND(kWh/cap., Swiss case) www.energyscope.ch

Major seasonal variations Transportation (th.)

Industry (th.)

Hot water (th.)

Heating (th.)

Transportation (el.)

Industry (el.)

Hot water (el.)

Heat pump (el.)

Heating (el.)

Other (el.)

DEMANDE ET PRODUCTION MENSUELLES D’ÉLECTRICITÉ (kWh/habitant, cas suisse) www.energyscope.ch

Consommation Stockage ?Stockage ?

Déficit hivernalDéficit hivernal

MONTHLY DEMAND & PRODUCTION OF ELECTRICITY (kWh/cap., Swiss future case)

Demand Storage ?Storage ?

Winter gapWinter gap

Seasonal StorageNuclearNatural GasCoalCogenerationSolar PVWindHydro (dam)Hydro (river)Geothermal

CODINAS GIRONES V., FAVRAT D. ET AL. Energy, 90 (PA1), pp. 173-186 (2015)

OPPORTUNITIES FOR ELECTRICITY STORAGE

Load balancing Peak shavingFrequency

controlSmoothing supply

Avoiding inefficient

partial loadsReducing rotating

reserves

Emergency supply

& “black start”

Power control

& capacity market

COMPETITION TO STORAGE

Power plant

overcapacity

Demand side managementSupergrids

Stopping productionGrid upgrade

STORAGE TYPES (TIME SCALE)

Seasonal

Elevation of hydraulic accumulation dams

Biomass and/or synthetic fuels

Heat and cold ground storage

Daily /

weekly

Hydro pump-turbine plants

Compressed air

Electric batteries (including of vehicles)

Hydrolyser+ H2 storage + engine/fuel cells

Thermal storage (hot water, ice, ground, molten

salts)

Rapid Supercap, flywheel, magneticFavrat D Webinar (in French)https://www.youtube.com/watch?v=mRsvd-T70o8

SEASONAL STORAGE

Height increase of dams- Storage of more water

- Better protection against floods

Synthetic fuels(gas or liquid)

From A.Züttel

Photo Ch. Ellena

ou CH4

Ex: alpine cheese

SYNTHESIS

CONVERSION

EFFICIENT USE OF SYNTHETIC FUELS: FUEL CELLS

See also Borel L, Favrat D., Thermodynamics and energy systems analysis, EPFL Press 2010

H2O, CO2 and non

oxidized fractions

Air depleted from

part of O2

REVERSIBLE FLOW FUEL CELLS:“Power to gas (SOEE)” and “gas to power (SOFC)”

HYBRID SOFC-GT FUEL CELL SYSTEM WITH CO2 SEPARATION

Water

Methane

Reactor

Anode

Cathode

Air

Fuel Processing Fuel Cell

Burner

Water

CO2

Air

Gas Turbine

Oxygen

LegendPump

Power

Compressor

Turbine Heat exchanger

Separator

Material Stream

Heat Stream

Fan

CO2, H2O

• A SOFC is inherently a separator of oxygen and nitrogen of air

• Anodic flow is mainly CO2 and H2O that can be used in a sub-

atmospheric Brayton cycle improving the overall electrical

efficiency (up to 80%) with an efficient CO2 recovery

FACCHINETTI E., FAVRAT D., MARECHAL F. Fuel cells 14,4, pp 595-606 (2014)

Advanced CO2 District

Heating and Cooling

Networks (DHCN)

Towards a city without cooling tower, nor chimneys (except at a

central plant): maximise the synergy between usersHENCHOZ S., FAVRAT D. ET AL. Energy, pp 1-13 (June 2016)

extensions

and transfer

through

CO2 network

DHCN

HENCHOZ S, FAVRAT D., ET AL. 12th IEA heat pump conference 2017, Rotterdam, May 2017

DAILY STORAGE 2Example: Storage through reversable flow cycles

Thermo-Electric Energy Storage

Assisted Charging

Storage charging:A heat-pump cycle consumes electricity from the grid and charges thermal storagesHot water tank can then be heated by solar or waste heat

Part of Master thesis Samuel Henchoz done at ABB research

Charge: heating storage water using heat pumps

Discharge: electricity production by engine cycles like ORC

Engine cycle (ORC)

Heat pump

Eau

CO2

Glace

MORANDIN M., FAVRAT D.,ET AL. Energy 58, p571-587 (2013)

DAILY STORAGERound trip efficiency and cost

100

90

80

70

60

50

400 1k 10k 100k

Ro

un

d trip

effic

iency [ %

]

Cycles

Plomb

À flux

AirComp

Pompage

-

turbinage

NiCd

Metal

air

NaS

Li-ion capacités

Volants Supercap

30k

10k

3k

1k

300

100

3010 100 300 1k 3k

Pump

.-turb.Compr.

air

Lead

FlowLi-ion

Specific power capacity cost [€/kW]S

pecific

energ

y c

apacity c

ost [€

/kW

h]

Rufer A, Energy storage, CRC Press 2018

NaS= Sodium-sulfer (both in liquid state at around 300°C)

CONCLUSION

• ELECTRICITY STORAGE IS A KEY ELEMENT OF THE ENERGY TRANSITION TOWARDS RENEWABLES

• DAILY ENERGY STORAGE, IN PARTICULAR OF ELECTRICITY, GROWS AT A HIGH PACE

• THERE IS A COMPETITION BETWEEN CENTRALIZED AND DECENTRALISED TECHNOLOGIES

• SEASONAL STORAGE REMAINS A MAJOR CHALLENGE (SYNTHETIC FUELS)

• REDUCING EMBEDDED ENERGY, AND MATERIAL RECYCLING REPRESENT ANOTHER CHALLENGE

Microgrids

Microgrids

Microgrids

Microgrids